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DOI: 10.1016/j.jcs.2017.04.005
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Model gluten gels

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DOI: 10.1039/c6sm00710d
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The structure of model gluten protein gels prepared in ethanol/water is investigated by small angle X-ray (SAXS) and neutrons (SANS) scattering. We show that gluten gels display radically different SAXS and SANS profiles when the solvent is (at least partially) deuterated. The detailed analysis of the SANS signal as a function of the solvent deuteration demonstrates heterogeneities of sample deuteration at different length scales. The progressive exchange between the protons (H) of the proteins and the deuteriums (D) of the solvent is inhomogeneous and 60 nm large zones that are enriched in H are evidenced. In addition, at low protein concentration, in the sol state, solvent deuteration induces a liquid/liquid phase separation. Complementary biochemical and structure analyses show that the denser protein phase is more protonated and specifically enriched in glutenin, the polymeric fraction of gluten proteins. These findings suggest that the presence of H-rich zones in gluten gels would arise from the preferential interaction of glutenin polymers through a tight network of non-exchangeable intermolecular hydrogen bonds.

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DOI: 10.1016/j.foodhyd.2015.06.014
WoS: 000363832300001
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26 Citations
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Structuring wheat gluten proteins into gels with tunable mechanical properties would provide more versatility for the production of plant protein-rich food products. Gluten, a strongly elastic protein material insoluble in water, is hardly processable. We use a novel fractionation procedure allowing the isolation from gluten of a water/ethanol soluble protein blend, enriched in glutenin polymers at an unprecedented high ratio (50%). We investigate here the viscoelasticity of suspensions of the protein blend in a water/ethanol (50/50 v/v) solvent, and show that, over a wide range of concentrations, they undergo a spontaneous gelation driven by hydrogen bonding. We successfully rationalize our data using percolation models and relate the viscoelasticity of the gels to their fractal dimension measured by scattering techniques. The gluten gels display self-healing properties and their elastic plateaus cover several decades, from 0.01 to 10,000 Pa. In particular very soft gels as compared to standard hydrated gluten can be produced.

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SANS study of a gluten protein gel: Why are SAXS and SANS profiles diffrents?

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Producing wheat gluten gels with tunable mechanical properties via simple sol-gel routes would facilitate their processing into plant protein-rich food products. However, standard gluten is a very elastic mass with a high concentration of proteins in water and is hardly processable except using high shear harsh extrusions. The wheat proteins are responsible for the viscoelastic properties of standard gluten and dough and are among the most complex proteins families, with extremely broad polymorphisms and polydispersities. They are moreover insoluble in water, rendering rational studies difficult. Thanks to a novel protocol for the gluten proteins extraction that we have recently developed, stable ethanolic suspensions of gluten proteins are obtained for a wide range of protein concentrations. In this talk, we will present the viscoelasticity of those suspensions and show that they exhibit a spontaneous and concentration-dependent gelation, which we find to be driven by the slow formation of hydrogen bonds. We successfully rationalize our data using percolation models and relate the viscoelasticity of the gels to their fractal dimension measured by scattering techniques. The novel gluten gels display self-healing properties and their elastic plateaus cover several decades, from 10-2 to 104 Pa. In particular very soft gels as compared to standard hydrated gluten, suitable for processing, can be produced.

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he supramolecular organization of wheat gluten proteins is largely unknown due to the intrinsic complexity of this family of proteins and their insolubility in water. We fractionate gluten in a water/ethanol (50/50 v/v) and obtain a protein extract which is depleted in gliadin, the monomeric part of wheat gluten proteins, and enriched in glutenin, the polymeric part of wheat gluten proteins. We investigate the structure of the proteins in the solvent used for extraction over a wide range of concentration, by combining X-ray scattering and multi-angle static and dynamic light scattering. Our data show that, in the ethanol/water mixture, the proteins display features characteristic of flexible polymer chains in a good solvent. In the dilute regime, the protein form very loose structures of characteristic size 150 nm, with an internal dynamics which is quantitatively similar to that of branched polymer coils. In more concentrated regimes, data highlight a hierarchical structure with one characteristic length scale of the order of a few nm, which displays the scaling with concentration expected for a semi-dilute polymer in good solvent, and a fractal arrangement at much larger length scale. This structure is strikingly similar to that of polymeric gels, thus providing some factual knowledge to rationalize the viscoelastic properties of wheat gluten proteins and their assemblies.